Fig. 1. Working principle diagram of COTDR system

Fig. 2. Detection signal at different moments. (a) Time t1; (b) time t2

Fig. 3. Schematic of optical scanning frequency extension at different moments. (a) Time t1; (b) time t2

Fig. 4. Optical frequency extension simulation. (a) Distribution curves of optical power signal intensity; (b) comparison of original data and optical frequency extension data; (c) range of optical frequency extension versus temperature change

Fig. 5. Experimental system of COTDR

Fig. 6. Cross-correlation curves before and after temperature change. (a) Cross-correlation curve of original data; (b) cross-correlation curve after optical frequency extension

Fig. 7. Cross-correlation curves before and after temperature change. (a) Cross-correlation curve of original data; (b) cross-correlation curve after optical frequency extension

Fig. 8. Temperature change versus time